The present invention relates to a device for measuring the volume of containers such as jars or bottles for quality control purposes, and a method for measuring the volume of the same.
Containers are formed by various methods of production and from various materials. Plastic containers can be formed by introducing a desired amount of material into a mold and then blowing air into the material to force it against the walls of the mold (blow molding) or by pulling a vacuum between the mold and the material to pull the material to the wall (thermoforming). Alternately, containers can be made by the injection molding process, or rotomolding. For glass containers, glass blowing is frequently used, as is well known and discussed in the patent art. Containers can also be fabricated from metal or other materials by various methods.
In the container manufacturing industry, it has been the practice to maintain consistency in the production of containers to assure that they meet the targeted volume capacity. For example, for molded containers, quality control techniques have been developed to determine whether the container material is adequately conforming to the walls of the mold. Meeting these requirements depends on whether certain process parameters, such as the temperature of the material and the conditions of the forming operation, are within tolerable limits. It has been found that measuring the volume of the resulting containers not only provides verification of this important parameter, but also provides an excellent way to determine whether the containers are adequately conforming to the mold walls and whether the containers will meet the targeted volumetric content when filled to a predetermined fill line.
Two different volume measurements are of concern when dealing with containers. The first is the ultimate, brimful volume of the containers, normally referred to as the OverFlow Capacity (OFC). The OFC includes the volume up to the upper rim of the opening. The second measurement is the Fill Line Volume (FLV), which is the volume to a fill line plane to which the container is intended to be filled. Thus, when the properly sized container is filled with liquid such that the surface of the liquid resides in the fill line plane when the container is upright, the volume of liquid equals the FLV. The FLV must meet the packaging target of such containers, and normally becomes a specified amount on the label of most products sold in containers. For monitoring production, once standard production parameters have been established, it is sufficient for quality control purposes to measure and control the OFC of the containers.
The standard method for determining the volume is to fill the container with water and weigh the container with and without the water, using the net water weight and its density to calculate the volume. This method requires filling the container consistently to a particular fill height, as well as making accurate measurements of both weight and temperature, the latter to compensate for changes in the water density. When performed manually, the method is very labor intensive and is subject to operator limitations, making repeatability problematic.
An alternative approach for determining volume is taught in U.S. Pat. No. 5,319,957, which teaches the use of a piston to compress air in the container being tested. The pressure in the container is sensed and the volume determined from the change in pressure. While this approach eliminates the need to fill the container precisely with liquid, it is extremely complicated and requires complex equipment and calculations to obtain the volume measurement. An additional problem is that many containers are sufficiently thin and flexible that the volume may change as the pressure inside the container is increased. Further, this method cannot be used for the determination of the volume to the fill line level.
Thus, there is a need for a simple device and method for measuring the volume of containers which does not require complex equipment or calculations, and which is independent of the exact volume of fluid employed for measuring.
The present invention provides a device and a method for measuring the volume of containers having a rim. The method is easily executed and the container volume measuring device is simple in structure and provides reliable results. The container volume measuring device has a reservoir of known volume having an upper bounding surface. Preferably, the known volume is comparable to but slightly larger than the volume of the containers to be measured.
A measuring tube is also provided. The measuring tube has a first end and a second end, and has a measuring tube passage which passes therebetween. The measuring tube passage has a passage volume greater than the difference in volume between the known volume of the reservoir and the volume range of the containers to be tested. The measuring tube is positioned such that the first end is sealably attached with respect to the reservoir such that the measuring tube passage communicates with the reservoir. It is preferred that first end of the measuring tube be at the bounding surface of the reservoir, since such will leave the known volume unobstructed. The measuring tube is also attached to a container mount which is configured to sealably engage the rim of the container. The container mount is attached to the measuring tube such that the measuring tube passage communicates with the container at the second end of the measuring tube when the container is attached to the container mount. The measuring tube passage is preferably configured such that the height of liquid in the measuring tube can be correlated to the volume of liquid contained therein. More preferably, the measuring tube passage has a constant cross section such that the height of liquid therein varies linearly with the volume of liquid residing in the measuring tube.
Means are provided for measuring the volume of liquid residing in the measuring tube. When the height of liquid in the measuring tube is correlated to the volume of liquid contained in the measuring tube passage, such means can be provided with various means for measuring the height of the liquid. In one embodiment, the measuring tube is provided with a window of sufficient size to allow the height of the liquid in the measuring tube to be viewed independently of whether the reservoir or the container is beneath the tube. The window in turn has indicia thereon, allowing an operator to visually measure the height of liquid in the measuring tube which is correlatable to the volume of the liquid in the measuring tube. When the tube passage has a constant cross section, the height of the liquid in the measuring tube will be directly proportional to the volume and the indicia can be used to read the volume directly.
The measuring tube is mounted to a support, which allows the measuring tube to be pivoted between two measuring orientations. Preferably, in each of the two measuring orientations the measuring tube is substantially vertical. In the first measuring orientation, the first end of the measuring tube is lower than the second end, while in the second measuring orientation, the first end is elevated above the second end. Preferably, stops are provided on the support to limit the motion of the measuring tube to prevent the measuring tube from being pivoted beyond the two measuring orientations.
When the measuring tube is oriented such that the first end of the measuring tube is lower than the second end, the reservoir and the measuring tube are filled with liquid such that the liquid partially fills the measuring tube. The volume of liquid is selected to be at least as great as the maximum volume of container anticipated. The volume of the liquid in the measuring tube is the excess volume of liquid equal to the difference in volume between the total volume of liquid and the known volume of the reservoir, and is defined as a first excess volume, which is associated with filling the reservoir.
When the container to be measured is attached to the container mount and the measuring tube is pivoted on the support to its second measuring orientation, where the first end of the measuring tube is higher than the second end, the liquid flows into the container. As noted above, the volume of liquid is selected to be at least as great as the volume of largest expected container being measured. Thus, when the measuring tube is pivoted to its second measuring orientation, the liquid again partially fills the measuring tube and establishes a second excess volume of liquid, which is associated with the container being filled. The second excess volume of liquid in the measuring tube equals the difference between the total volume and the volume of the container.
Since the total volume of liquid remains constant, the difference between the first excess volume, which is associated with filling the reservoir, and the second excess volume, which is associated with filling the container, is equal to the difference between the volume of the container and the known volume of the reservoir. Since the volume of the reservoir is known, the volume of the container can then be calculated from the difference in volume of the liquid in the measuring tube. The calculation of the container volume can be done by the operator or, when the volume of liquid in the measuring tube is measured by a sensor or other instrumentation, the calculations can be done by a microprocessor to which the means for measuring the volume of liquid reports its output. Since only the difference in volume is employed in the calculation, the measurement does not depend on the reservoir and the measuring tube being filled with any particular total volume of liquid. This eliminates any need for precision in filling the reservoir and the measuring tube, and makes operation of the device independent of any slight loss of liquid over time due to spillage and/or evaporation.
While the discussion thus far has been general, the container volume measuring device can measure OverFlow Capacity (OFC) without further adaptations. This is the mode of operation when the second end of the measuring tube is mounted in the container mount such that it resides in the plane of the rim of the container when the container is attached to the container mount.
When the container volume measuring device is designed to measure Fill Line Volume (FLV), where the container is to be filled to a fill line plane which is below the rim, the second end of the measuring tube is positioned with respect to the container mount such that the second end resides at the fill line plane of the container when the container is attached to the container mount. As the measuring tube is pivoted on the support to its second measuring orientation, where the first end of the measuring tube is higher than the second end, the liquid flows from the reservoir into the container until the liquid reaches the fill line. As the liquid flows into the container, it displaces the air in the container, which exits the container via the second end of the measuring tube. When the liquid reaches the fill line, it engages the second end of the measuring tube and blocks the further passage of air therethrough. The remaining air is trapped in the container and cannot escape, so further flow of liquid into the container compresses the air until the pressure inside the container and the static pressure of the column of liquid in the measuring tube reach equilibrium, at which time the liquid ceases to flow into the container. Since the height of liquid in the measuring tube is relatively low, the pressure required to maintain such height of liquid is low, and the liquid ceases flowing when the height of liquid in the container is substantially at the fill line plane. In this situation, the difference in excess volume of liquid in the measuring tube allows calculation of the fill line volume of the container.
In this embodiment, where the second end of the measuring tube is positioned at the fill line plane of the container, most of the liquid in the container flows back into the reservoir through the measuring tube passage when the measuring tube is pivoted back to its first measuring orientation. However, a portion of liquid becomes trapped in the upper portion of the container between the fill line plane and the rim of the container. This residual liquid needs to be drained before another measurement is taken. For this reason, when the second end of the measuring tube is positioned at the fill line plane, it is preferred that a drain passage be provided, the drain passage connecting the container mount to the measuring tube passage and being so positioned as to drain the residual liquid. An intermittently operable drain valve is provided to control the flow of liquid through the drain passage. The drain valve is activated to provide passage of liquid through the container mount bypassing the second end of the measuring tube either selectively or, more preferably, automatically when the measuring tube is pivoted back to its first measuring orientation. When the drain valve is closed, passage of fluids through the container mount is restricted to the measuring tube passage.
As noted above, an automatic recording mechanism can be employed for measuring and reporting the excess volumes of the liquid in the measuring tube. In such cases, the output of this instrumentation is preferably provided to a microprocessor programmed to calculate the volume of the container. In one automated system a temperature sensor is provided, and the output from the temperature sensor provided to the microprocessor to allow correcting the calculated volume for the temperature in the event that the reservoir, the measuring tube, and the container are constructed from materials having different thermal expansions. When a microprocessor is employed for calculating the volume of the container, the microprocessor can also be programmed to compare the calculated value to a design volume range to determine whether the calculated volume of the container falls within acceptable limits. When a series of containers are measured, the microprocessor can also be programmed to provide statistical analysis of the container volumes for traditional quality control techniques.
While the volume measuring devices discussed above can be designed to be suitable for determining the volume of containers having a limited variation in size, it is frequently desirable to measure containers having a large distribution of sizes. In such cases, it is preferred for the known volume of the reservoir to be adjustable to accommodate an amount of liquid suitable for measuring different sizes of containers. Flexibility in the capacity of the reservoir can be obtained by means for adjusting the volume of the reservoir. There are a variety of elements which could provide such means, such as a series of reservoirs having various known volumes and a reservoir coupling attaching to the first end of the measuring tube. Alternatively, a reservoir which allows its internal volume to be collapsed or expanded in a known manner could be employed.
It is preferred for the reservoir which is expandable or collapsible to employ two chambers having reciprocally collapsible or expandable volumes and a valve to control flow of liquid between the chambers. One of the chambers, defined as an active chamber, communicates with the measuring tube passage at the first end of the measuring tube and serves to provide a known volume for reference in the manner of the reservoir discussed above. Such reciprocally changeable chambers may be provided by separating the chambers by a piston. As the piston moves to collapse one chamber, its motion correspondingly expands the other chamber.
It is also preferred for the container mount to be adaptable to accept different configurations of container rims by employing a number of container rim adapters. The container mount can employ interchangeable container rim adapters, each of which is attachable to the container mount, or interchangeable container mounts can be employed which are each attachable to the measuring tube, in which case the container rim adapters are each integral with an associated one of the container mounts. Each container rim adapter is designed to mate with a particular configuration of container rim. When multiple, interchangeable container rim adapters are employed, they are preferably designed such that their internal volume, if any, is known to allow for correction of its effect on the perceived container volume so that the difference in height of liquid in the measuring tube continues to correspond to the difference in volume between the container and the reservoir. Alternatively, the container rim adapters can each have a particular known internal volume, which is subtracted when calculating the container volume.
In a preferred embodiment, the measuring tube passage has both a flow passage and a measurement passage. The flow passage extends between the second end of the measuring tube and the reservoir, and has a relatively large cross section to allow the flow of liquid and displaced air therethrough. The measurement passage is smaller in cross section than the flow passage, and extends substantially therealong. The measurement passage communicates with the flow passage such that the height of liquid in both passages is the same. In this embodiment, the means for measuring the excess volume of liquid in the measuring tube is associated with the measurement passage. When the means for measuring the excess volume of liquid is visual or optical in nature, this structure eliminates any requirement for viewing through the flow passage, allowing it to be constructed of a stronger material for improved durability of the resulting device.
In all cases, it is preferred for the measuring tube passage to have a cross section sufficiently small that significant differences in volume result in readily apparent differences in height. However, limiting the cross section of the measuring tube passage can impede the flow of liquid and displaced air between the reservoir and the container when the measuring tube is pivoted between its two orientations. To promote uninterrupted flow of liquid when the measuring tube is pivoted, thus speeding the measurement process, it is preferred that the device be provided with a means for promoting steady flow of liquid and air past each other through the measuring tube between the reservoir and the container.
In one embodiment, a flow enhancement passage extends between the reservoir and the container mount to allow free flow of air between the container and the reservoir. The flow enhancement passage preferably extends a substantial distance into the reservoir to facilitate flow of air into the reservoir. In the event that the flow enhancement passage extends into the container, its volume as well as for the volume of liquid it will hold must be compensated for when calculating the differential volume. Such compensation is preferably incorporated into the particular means for measuring the volume which is employed. When FLV is to be measured, the flow enhancement passage extends into the container to or somewhat beyond the fill line plane. Preferably, the flow enhancement passage extends only to the fill line plane in this case, to avoid the requirement to compensate for the volume taken up by the portion of the flow enhancement passage extending beyond the fill line plane.
In an alterative embodiment offering enhanced flow, the support is provided with one or more detents to interrupt the pivoting of the measuring tube when the measuring tube is rotated between the two measuring orientations. The detent interrupts pivoting when the measuring tube is in a substantially non-vertical orientation, to aid in the air and the liquid to freely flow past each other. The measuring tube can then be pivoted past the substantially non-vertical orientation to one of its measuring orientations. Preferably two non-vertical positions are provided, each of which is nearly horizontal with one of the reservoir and the container positioned slightly below the other to promote the flow of liquid therebetween.
Other schemes for slowing or temporarily interrupting the rotation of the measuring tube to allow the air time to escape freely will be apparent. For example, a frictional engagement between the measuring tube and the support can be employed, which is overcome by gravity as the liquid shifts between the reservoir and the container. In automated systems, an electro-mechanical drive can be effectively employed to pivot the measuring tube in a desired manner.
In all of the above embodiments, it is preferred for a surfactant to be added to the liquid to reduce the surface tension between the liquid and the interior of the reservoir to promote drainage of liquid therefrom.
To practice the method of the present invention to measure the unknown volume of a container, a measuring tube having one of its ends connected to a reservoir of known volume is provided. Preferably, the measuring tube is configured with a constant cross section to allow the height of the liquid in the measuring tube to be correlated to the volume of liquid residing therein. The reservoir and the measuring tube are oriented such that the reservoir resides below at least a part of the measuring tube. When so positioned, a volume of liquid somewhat greater than the known volume of the reservoir is introduced into the reservoir and the measuring tube, such that the liquid partially fills the measuring tube.
Preferably, the measuring tube is moved to a substantially vertical orientation, if not already so oriented. The volume of liquid in the measuring tube is measured and recorded as a first excess volume of liquid. The first excess volume of the liquid correlates to the total volume of liquid, which consists of the known volume of liquid in the reservoir and the excess volume of liquid which resides in the measuring tube in this orientation (Vtube1).
Vtotal=Vreservoir+Vtube1xe2x80x83xe2x80x83(Equation 1)
The container to be measured is mounted to the measuring tube so as to communicate with the end of the measuring tube that is not connected to the reservoir. It should be appreciated that the measurement of the first excess volume could be made after attaching the container to the end of the measuring tube.
The container, the measuring tube, and the reservoir are then substantially inverted to elevate the reservoir substantially above the container. Preferably, the measuring tube is again substantially vertically oriented. The volume of the liquid in the measuring tube is again measured, this value being recorded as a second excess volume. The second excess volume of the liquid again correlates to the total volume of liquid, which consists of the unknown volume of liquid in the container and the excess volume of liquid which resides in the measuring tube in this orientation (Vtube2).
Vtotal=Vcontainer+Vtube2xe2x80x83xe2x80x83(Equation 2)
The difference between the first excess volume of liquid and the second excess volume of liquid can be calculated by subtraction. For example:
xcex94V=Vtube1xe2x88x92Vtube2xe2x80x83xe2x80x83(Equation 3)
Since the total volume remains constant, the difference in excess volume of liquid in the measuring tube is equal to the difference in volume between the container and the reservoir, and the unknown volume of the container can be calculated from the difference in excess volume of liquid and the known volume of the reservoir. One scheme for determining the volume of the container from the volume of the reservoir and the difference in excess volume is shown in the following equations:
Vtotal=Vreservoir+Vtube1=Vcontainer+Vtube2xe2x80x83xe2x80x83(Equation 4)
Vcontainer=Vreservoir+Vtube1xe2x88x92Vtube2xe2x80x83xe2x80x83(Equation 5)
Vcontainer=Vreservoir+xcex94Vxe2x80x83xe2x80x83(Equation 6)
After the second excess volume has been measured, the volume of the container can be calculated. After this measurement, the container, the measuring tube, and the reservoir can then be reinverted to elevate the container substantially above the reservoir. The container can then be removed while the liquid is retained in the reservoir and the measuring tube. A new container to be measured can then be mounted to the measuring tube and the method repeated to measure the volume of the new container.